The first filial generation produced by crossing two parental strains. A condition in some hominid faces where the nasal bones and the borders of the piriform aperture are recessed relative to the cheeks, making the midface area concave. A multivariate statistical technique which assesses the degree of variation between artifact types, and is based on a matrix of correlation coefficients which measure the relative association between any two variables. Chromatin that may become condensed throughout the cell cycle and may contain genes that are inactivated when the chromatin becomes condensed. The study of regularities in the way in which quantities of traded items found in the archaeological record decline as the distance from the source increases. This may be plotted as a fall-off curve, with the quantities of material Y-axis plotted against the distance from the source X-axis. A trait shared by members of a family. The major group within an order, a monophyletic group of genera separated from similar groups by distance of common ancestry. A group of living or fossil animals found in a particular geographic or geological context, thought to sample part of a naturally occurring community. Determination of the relative ages of different geological strata by comparing the fossils within the strata and assigning similar ages to strata with similar fossils; a method of relative dating.
Principle of faunal succession
A Abbreviations This information is included in Appendix A: Abbreviations , which includes all abbreviations and acronyms used in the Factbook, with their expansions. Acronyms An acronym is an abbreviation coined from the initial letter of each successive word in a term or phrase.
evolution of the arctic-north atlantic and the western tethys–a visual presentation of a series of paleogeographic-paleotectonic maps*, peter a. ziegler.
General considerations Distinctions between relative-age and absolute-age measurements Local relationships on a single outcrop or archaeological site can often be interpreted to deduce the sequence in which the materials were assembled. This then can be used to deduce the sequence of events and processes that took place or the history of that brief period of time as recorded in the rocks or soil.
For example, the presence of recycled bricks at an archaeological site indicates the sequence in which the structures were built. Similarly, in geology, if distinctive granitic pebbles can be found in the sediment beside a similar granitic body, it can be inferred that the granite, after cooling, had been uplifted and eroded and therefore was not injected into the adjacent rock sequence.
Although with clever detective work many complex time sequences or relative ages can be deduced, the ability to show that objects at two separated sites were formed at the same time requires additional information. A coin, vessel, or other common artifact could link two archaeological sites, but the possibility of recycling would have to be considered. It should be emphasized that linking sites together is essential if the nature of an ancient society is to be understood, as the information at a single location may be relatively insignificant by itself.
Who Were the First Americans?
From where did they come and what routes did they take? These questions have gripped scientists for decades, but until recently answers have proven difficult to find. New techniques of molecular genetic analysis, and a reinvigorated search for early archaeological sites across the western hemisphere, recently have led to some astounding results. The route taken by the first explorers appears to have been along the recently deglaciated north Pacific coastline.
Until recently, it was generally believed that about Today, we realize that the peopling of the Americas was a much more complex process, because of two significant developments that occurred during the past decade.
ASSISTED COLONIZATION is the intentional movement and release of an organism outside its indigenous range to avoid extinction of populations of the focal species.. ECOLOGICAL REPLACEMENT is the intentional movement and release of an organism outside its indigenous range to perform a specific ecological function.. See the 3-fold chart immediately below for distinctions between three forms of.
A Abbreviations This information is included in Appendix A: Abbreviations , which includes all abbreviations and acronyms used in the Factbook, with their expansions. Acronyms An acronym is an abbreviation coined from the initial letter of each successive word in a term or phrase. In general, an acronym made up of more than the first letter of the major words in the expanded form is rendered with only an initial capital letter Comsat from Communications Satellite Corporation; an exception would be NAM from Nonaligned Movement.
Administrative divisions This entry generally gives the numbers, designatory terms, and first-order administrative divisions as approved by the US Board on Geographic Names BGN. Changes that have been reported but not yet acted on by the BGN are noted. Geographic names conform to spellings approved by the BGN with the exception of the omission of diacritical marks and special characters.
Age structure This entry provides the distribution of the population according to age. Information is included by sex and age group as follows: The age structure of a population affects a nation’s key socioeconomic issues. Countries with young populations high percentage under age 15 need to invest more in schools, while countries with older populations high percentage ages 65 and over need to invest more in the health sector.
The age structure can also be used to help predict potential political issues. For example, the rapid growth of a young adult population unable to find employment can lead to unrest.
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The following list summarizes the criteria: The lower boundary has to be defined using a primary marker usually first appearance datum of a fossil species. There should also be secondary markers other fossils, chemical , geomagnetic reversal.
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Making the transition to the third era of natural resources management , by Nathan L. This is an ideal paper for probing the psychological anguish that accompanies the pragmatic shift in conservation paradigms forced by rapid climate change. The author has worked in Sequoia and Kings Canyon National Park for 35 years, and he wrote this essay as a contribution to the National Park Service Centennial in This third era promises to overturn not only some of our most fundamental assumptions about parks and protected areas, but also many of the ideals we currently hold dear.
A common initial reaction to the diverse challenges of this transition is to feel overwhelmed and adrift; I have certainly had such feelings myself. But these feelings carry the risk of reducing our effectiveness as resource stewards right when we can least afford to be less effective: Here I briefly examine some of the challenges of this new era, focusing on those that can most often elicit feelings of discouragement.
A researcher who specialized in cells and microorganisms, Margulis was one of the most important biologists in the last half century—she literally helped to reorder the tree of life, convincing her colleagues that it did not consist of two kingdoms plants and animals , but five or even six plants, animals, fungi, protists, and two types of bacteria. She knew I was interested in ecology, and she liked to needle me. Hey, Charles, she would call out, are you still all worked up about protecting endangered species?
Margulis was no apologist for unthinking destruction.
Is this worth reading – is it True? On the matter of credibility: On first reading, readers of these pages generally feel amazement, the concept of Blacks being the original settlers, and builders of the first civilizations everywhere, including Europe, is particularly unsettling to them.
Cultural History This overview of the prehistory and history of southeastern New Mexico, specifically the lower Pecos River to the Texas border, is designed to address two areas. First, this overview will briefly outline broad temporal periods and mention some of the previous fieldwork that was used in their definition in southeastern New Mexico. A discussion section follows and addresses theoretical and methodological issues that affect our knowledge of that temporal period.
The methodological discussion includes information that can be derived from survey and excavation. The beginning of human occupation of the eastern slopes of the Sacramento Mountains is unknown. Evidence for limited use of the area from at least 20, years ago has been documented from Pendejo Cave located on the eastern edge of the Tularosa Basin MacNeish and Libby The earliest record of human occupation in southern New Mexico is indicated by the occurrence of generalized lithic toolkits associated with the remains of Pleistocene mammals and plants with radiocarbon dates ranging back to forty thousand years ago at Pendejo Cave near Oro Grande MacNeish and Libby With the exception of a possibly earlier complex from Hermit’s Cave, the Paleoindian period in southeastern New Mexico is characterized by distinctive lanceolate projectile points.
Sites with Paleoindian components have been recovered from lower elevations in areas that have been exposed through erosion. These types of Paleoindian points have been recovered as isolated finds, in association with later occupations, and with extinct Pleistocene fauna Hammack ; Hester By examining the contexts of these different kinds of discovery situations in the Pecos drainage of New Mexico, some suggestions can be made regarding the chances for the recovery of Paleoindian remains within that region.
Much has been made of the presence of Paleoindian remains occurring in areas subject to erosion Cordell Most Paleoindian sites in southern New Mexico bear this out. Soils within the proposed survey area are sandy loams or loamy sands, are often shallow, and subject to erosion Maker et al.
Great American Interchange
Tertiary mammals of the western United States 4. Tertiary bird and mammal tracks and the Devils corkscrews 5. Tertiary volcanism in the northwest United States 6. The cooling of ocean basalt while the continents rise Table 1. Why is the boundary important? Creationists are interested in identifying the post-Flood boundary for several reasons.
Dating: Dating, in geology, determining a chronology or calendar of events in the history of Earth, using to a large degree the evidence of organic evolution in the sedimentary rocks accumulated through geologic time in marine and continental environments. To date past events, processes, formations, and.
Tweet methods dates sample age Dating techniques are procedures used by scientists to determine the age of a specimen. Relative dating methods tell only if one sample is older or younger than another; absolute dating methods provide a date in years. The latter have generally been available only since Many absolute dating techniques take advantage of radioactive decay , whereby a radioactive form of an element is converted into a non-radioactive product at a regular rate.
Others, such as amino acid racimization and cation-ratio dating, are based on chemical changes in the organic or inorganic composition of a sample. In recent years, a few of these methods have come under close scrutiny as scientists strive to develop the most accurate dating techniques possible. Relative dating methods determine whether one sample is older or younger than another.
They do not provide an age in years. Before the advent of absolute dating methods, nearly all dating was relative. The main relative dating method is stratigraphy. Absolute dating is the term used to describe any dating technique that tells how old a specimen is in years. These are generally analytical methods, and are carried out in a laboratory. Absolute dates are also relative dates, in that they tell which specimens are older or younger than others.
Fossils succeed each other vertically in a specific, reliable order that can be identified over wide horizontal distances For the principal of ecological success following disturbance, see ecological succession. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources.
Unsourced material may be challenged and removed. February Learn how and when to remove this template message The principle of faunal succession, also known as the law of faunal succession, is based on the observation that sedimentary rock strata contain fossilized flora and fauna , and that these fossils succeed each other vertically in a specific, reliable order that can be identified over wide horizontal distances.
The Great American Interchange was an important late Cenozoic paleozoogeographic event in which land and freshwater fauna migrated from North America via Central America to South America and vice versa, as the volcanic Isthmus of Panama rose up from the sea floor and bridged the formerly separated gh there were earlier dispersals, probably over water, the migration accelerated.
Each proxy material differs according to: Some proxy records, for example ocean floor sediments, reveal information about long periods of climatic change and evolution years , with a low-frequency resolution years. Others, such as tree rings are useful only during the last 10, years at most, but offer a high frequency annual resolution. The choice of proxy record as with the choice of instrumental record very much depends on what physical mechanism is under review.
As noted, climate responds to different forcing mechanisms over different time scales, and proxy materials will contain necessary climatic information on these to a greater or lesser extent, depending on the three factors mentioned. Other factors that have to be considered when using proxy records to reconstruct palaeoclimates include the continuity of the record and the accuracy to which it can be dated Bradley, Ocean sediments may provide continuous records for over 1 million years Ma but typically they are hard to date using existing techniques.
Ice cores are easier to date but may miss layers from certain periods due to melting and wind erosion. Glacial deposits are highly episodic in nature, providing evidence only of discrete events in the past. Different proxy systems also have different levels of inertia with respect to climate, such that some systems may vary exactly in phase with climate whereas others lag behind by as much as several centuries e.
Like climate construction from instrumental records, palaeoclimate reconstruction may be considered to proceed through a number of stages Hecht et al.
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Most of us who follow the mysteries are aware that huge numbers of carcasses of extinct megafauna, notably mammoths, have been found preserved in the permafrost of Siberia — the victims, it has been suggested, of some great cataclysm near the end of the last Ice Age. Most of us are also probably aware that similar claims have been made for Alaska; however, the evidence there has received less attention.
It is this mystery, the so-called terminal Ice Age cataclysm and megafaunal extinctions of Alaska, that I want to take a look at here — hopefully with your help. If anyone reading this has done any relevant research or can shed any further light on the subject, please tell me what you know in the comments section below.
Writing in the April issue of American Antiquity, for example, Rainey, a professor of anthropology at the University of Alaska, described wide cuts, miles long and up to feet deep, that were then being sluiced out by the gold mining industry along stream valleys tributary to the Tanana river in Fairbanks District: No adequate explanation of the age of these deposits nor the manner in which they were formed can be given at present.
The Genetic Evidence. Old World Origins. All human skeletal remains from the Americas are anatomically modern Homo sapiens; thus the peopling of the New World is best understood in the context of the evolution and dispersal of modern humans in the Old human dispersal from Africa across Eurasia began by c. 50 ka and culminated with colonization of the Americas.
General features Diversity The evolution of the class Mammalia has produced tremendous diversity in form and habit. Living kinds range in size from a bat weighing less than a gram and tiny shrews weighing but a few grams to the largest animal that has ever lived, the blue whale , which reaches a length of more than 30 metres feet and a weight of metric tons nearly short [U. Every major habitat has been exploited by mammals that swim, fly, run, burrow, glide, or climb. The rodents order Rodentia are the most numerous of existing mammals, in both number of species and number of individuals, and are one of the most diverse of living lineages.
In contrast, the order Tubulidentata is represented by a single living species, the aardvark. The Uranotheria elephants and their kin and Perissodactyla horses , rhinoceroses , and their kin are examples of orders in which far greater diversity occurred in the late Paleogene and Neogene periods about 30 million to about 3 million years ago than today.